Epistemic Spot Check: Fatigue and the Central Governor Module

Link post

Epistemic spot checks used to be a se­ries in which I read pa­pers/​books and in­ves­ti­gated their claims with an eye to­wards as­sess­ing the work’s cred­i­bil­ity. I be­came un­happy with the limi­ta­tions of this pro­cess and am work­ing on cre­at­ing some­thing bet­ter. This post about both the re­sults of ap­ply­ing the in-de­vel­op­ment pro­cess to a par­tic­u­lar work, and ob­ser­va­tions on the pro­cess. As is my new cus­tom, this dis­cus­sion of the pa­per will be mostly my con­clu­sions. The ac­tual re­search is available in my Roam database (a work­flowy/​wiki hy­brid), which I will link to as ap­pro­pri­ate.

This post started off as an epistemic spot check of Fa­tigue is a brain-de­rived emo­tion that reg­u­lates the ex­er­cise be­hav­ior to en­sure the pro­tec­tion of whole body home­osta­sis, a sci­en­tific ar­ti­cle by Ti­mothy David Noakes. I don’t trust my­self to sum­ma­rize it fairly (we’ll get to that in a minute), so here is the ab­stract:

An in­fluen­tial book writ­ten by A. Mosso in the late nine­teenth cen­tury pro­posed that fa­tigue that “at first sight might ap­pear an im­perfec­tion of our body, is on the con­trary one of its most mar­velous perfec­tions. The fa­tigue in­creas­ing more rapidly than the amount of work done saves us from the in­jury which lesser sen­si­bil­ity would in­volve for the or­ganism” so that “mus­cu­lar fa­tigue also is at bot­tom an ex­haus­tion of the ner­vous sys­tem.” It has taken more than a cen­tury to con­firm Mosso’s idea that both the brain and the mus­cles al­ter their func­tion dur­ing ex­er­cise and that fa­tigue is pre­dom­i­nantly an emo­tion, part of a com­plex reg­u­la­tion, the goal of which is to pro­tect the body from harm. Mosso’s ideas were sup­planted in the English liter­a­ture by those of A. V. Hill who be­lieved that fa­tigue was the re­sult of bio­chem­i­cal changes in the ex­er­cis­ing limb mus­cles – “periph­eral fa­tigue” – to which the cen­tral ner­vous sys­tem makes no con­tri­bu­tion. The past decade has wit­nessed the grow­ing re­al­iza­tion that this brain­less model can­not ex­plain ex­er­cise perfor­mance.This ar­ti­cle traces the evolu­tion of our mod­ern un­der­stand­ing of how the CNS reg­u­lates ex­er­cise speci­fi­cally to in­sure that each ex­er­cise bout ter­mi­nates whilst home­osta­sis is re­tained in all bod­ily sys­tems. The brain uses the symp­toms of fa­tigue as key reg­u­la­tors to in­sure that the ex­er­cise is com­pleted be­fore harm de­vel­ops.Th­ese sen­sa­tions of fa­tigue are unique to each in­di­vi­d­ual and are illu­sion­ary since their gen­er­a­tion is largely in­de­pen­dent of the real biolog­i­cal state of the ath­lete at the time they de­velop.The model pre­dicts that at­tempts to un­der­stand fa­tigue and to ex­plain su­pe­rior hu­man ath­letic perfor­mance purely on the ba­sis of the body’s known phys­iolog­i­cal and metabolic re­sponses to ex­er­cise must fail since sub­con­scious and con­scious men­tal de­ci­sions made by win­ners and losers, in both train­ing and com­pe­ti­tion, are the ul­ti­mate de­ter­mi­nants of both fa­tigue and ath­letic performance

The eas­ily defen­si­ble ver­sion of this claim is that fa­tigue is a feel­ing in the brain. The most out there ver­sion of the claim is that hu­mans are ca­pa­ble of un­limited phys­i­cal feats, held back only by their own mind, and the re­sults of sport­ing events are de­ter­mined be­fore­hand through psy­chic dom­i­nance com­pe­ti­tions. That sounds like I’m be­ing un­fair, so let me quote the rele­vant portion

[A]thletes who finish be­hind the win­ner may make the con­scious de­ci­sion not to win, per­haps even be­fore the race be­gins. Their de­cep­tive symp­toms of “fa­tigue” may then be used to jus­tify that de­ci­sion. So the win­ner is the ath­lete for whom defeat is the least ac­cept­able rationalization

(He doesn’t men­tion psy­chic dom­i­nance com­pe­ti­tions ex­plic­itly, but it’s the only way I see to get ex­actly one per­son de­cid­ing to win each race).

This pa­per gen­er­ated a lot of ESC-able claims, which you can see here. Th­ese were un­usu­ally crisp claims that he pro­vided cita­tions for: ab­solutely the eas­iest thing to ESC (hav­ing your own cita­tions agree with your sum­mary of them is not suffi­cient to prove cor­rect­ness, but lack of it takes a lot works out). But I found my­self un­en­thused about do­ing so. I even­tu­ally re­al­ized that I wanted to read a com­pet­ing ex­pla­na­tion in­stead. Luck­ily Noakes pro­vided a cita­tion to one, and it was even more an­tag­o­nis­tic to him than he claimed.

VO2,max: what do we know, and what do we still need to know?, by Ben­jamin D. Lev­ine takes sev­eral di­rect shots at Noakes, in­clud­ing:

For the pur­poses of fram­ing the de­bate, Dr Noakes fre­quently likes to place in­ves­ti­ga­tors into two camps: those who be­lieve the brain plays a role in ex­er­cise perfor­mance, and those who do not (Noakes et al. 2004b). How­ever this straw man is specious. No one dis­putes that ‘the brain’ is re­quired to re­cruit mo­tor units – for ex­am­ple, spinal cord-in­jured pa­tients can’t run. There is no doubt that mo­ti­va­tion is nec­es­sary to achieve VO2,max. A sub­ject can elect to sim­ply stop ex­er­cis­ing on the tread­mill while walk­ing slowly be­cause they don’t want to con­tinue; no mys­ti­cal ‘cen­tral gov­er­nor’ is re­quired to hy­poth­e­size or pre­dict a VO2 be­low max­i­mal achiev­able oxy­gen trans­port in this case.

Which I would sum­ma­rize as “of course fa­tigue is a brain-me­di­ated feel­ing: you feel it.”

I stopped read­ing at this point, be­cause I could no longer tell what the differ­ence be­tween the hy­pothe­ses was. What are the ac­tual differ­ences in pre­dic­tions be­tween “your mus­cles are phys­i­cally un­able to con­tract?” and “your brain tells you your mus­cles are un­able to con­tract”? After think­ing about it for a while, I came up with a few:

  1. The former sug­gests that there’s no in­ter­me­di­ate be­tween “safely work­ing” and “in­ca­pac­i­ta­tion”.

  2. The lat­ter sug­ges­tions that you can get phys­i­cal gains through men­tal changes alone.

  3. And that this might lead to tis­sue dam­age as you push your­self be­yond safe limits.

Without look­ing at any ev­i­dence, #1 seems un­likely to be true. Things rarely work that way in gen­eral, much less in bod­ies.

The strongest pieces of ev­i­dence for #2 and #3 isn’t ad­dressed by ei­ther pa­per: cases when men­tal changes have caused/​al­lowed peo­ple to in­flict se­ri­ous in­juries or even death to them­selves.

  1. Hys­ter­i­cal strength (aka mom lifts car off baby)

  2. In­vol­un­tary mus­cle spasms (from e.g., seizures or old-school ECT)

  3. Stiff-man syn­drome.

So I checked these out.

Hys­ter­i­cal strength has not been stud­ied much, prob­a­bly be­cause IRBs are touchy about trap­ping ba­bies un­der cars (with an op­tion on “I was un­able to find the med­i­cal term for it). There are enough anec­dotes that it seems likely to ex­ist, al­though it may not be com­mon. And it can cause mus­cle tears, ac­cord­ing to sev­eral source­less cita­tions. This is sug­ges­tive, but if I was on Lev­ine’s team I’d definitely find it in­suffi­cient.

Most in­juries from seizures are from fal­ling or hit­ting some­thing, but it ap­pears pos­si­ble for in­juries to re­sult from over­ac­tive mus­cles them­selves. This is com­pli­cated by the fact that anti-con­vul­sant med­i­ca­tions can cause bone thin­ning, and by the fact that some un­known per­centage of all peo­ple are walk­ing around with frac­tures they don’t know about.

Un­mod­ified elec­tro-con­vul­sive ther­apy had a small but per­sis­tent risk of bone frac­tures, mus­cle tears, and join dis­lo­ca­tion. Newer forms of ECT use mus­cle re­lax­ants speci­fi­cally to pre­vent this.

Stiff-man Syn­drome: Wikipe­dia says that 10% of stiff-man syn­drome pa­tients die from aci­do­sis or au­to­nomic dys­func­tion. Aci­do­sis would be re­ally ex­cit­ing- ev­i­dence that overex­er­tion of mus­cles will ac­tu­ally kill you. Un­for­tu­nately when I tried to track down the cita­tion, it went nowhere (with one pa­per in­ac­cessible). Ad­di­tion­ally, one can come up with other ex­pla­na­tions for the aci­do­sis than mus­cle ex­er­tion. So that’s not com­pel­ling.

Over­all it does seem clear that (some) peo­ple’s mus­cles are strong enough to break their bones, but are stopped from do­ing so un­der nor­mal cir­cum­stances. You could call this vin­di­ca­tion for Noake’s Cen­tral Gover­nor Model, but I’m hes­i­tant. It doesn’t prove you can safely get gains by chang­ing your mind­set alone. It doesn’t prove all races are de­ter­mined by psy­chic dom­i­nance fights. Yes, Noakes was spec­u­lat­ing when he pos­tu­lated that, but with­out it his the­ory is some­thing like “you no­tice when your mus­cles reach their limits”. When you can safely push what feel like phys­i­cal limits on the mar­gin feels like a ques­tion that will vary a lot by in­di­vi­d­ual and that nei­ther pa­per tried to an­swer.

Over­all, Fa­tigue is a brain-de­rived emo­tion that reg­u­lates the ex­er­cise be­hav­ior to en­sure the pro­tec­tion of whole body home­osta­sis nei­ther passed nor failed epistemic spot checks as origi­nally con­ceived, be­cause I didn’t check its spe­cific claims. In­stead I thought through its im­pli­ca­tions and in­ves­ti­gated those, which sup­ported the weak but not strong form of Noake’s ar­gu­ment.

In terms of pro­cess, the key here was feel­ing and rec­og­niz­ing the feel­ing that in­ves­ti­gat­ing for­ward (eval­u­at­ing the im­pli­ca­tions of Noake’s ar­gu­ments) was more im­por­tant than in­ves­ti­gat­ing back­wards (the ev­i­dence Noake pro­vided for his hy­poth­e­sis). I don’t have a good ex­pla­na­tion for why that felt right at this time, but I want to track it.